How Size-Dependent Aerosol Surface Tension Descriptions Impact Predictions of Hygroscopic Growth and Cloud Droplet Activation
EMILY WERNER, Makaila Hammond, Alison Bain, Oregon State University
Abstract Number: 630
Working Group: Aerosol Chemistry
Abstract
One of the largest uncertainties in climate models and understanding Earth’s energy budget comes from the lack of understanding of atmospheric aerosols. Atmospheric aerosols can be a combination of liquid and solid particulate matter suspended in the atmosphere that have different chemical compositions and distributions. When surface active molecules are present in atmospheric aerosol, a reduced surface tension during hygroscopic growth may reduce the cloud droplet activation barrier. Here, we apply KÓ§hler calculations to droplets containing one of two surfactants, Triton X-100 or sodium octanoate, mixed with NaCl and glucose, and predict their surface tension during hygroscopic growth. We compare a computationally inexpensive, simple kinetic model that predicts both the size- and concentration-dependent surfactant partitioning during hygroscopic growth to assuming a surface tension of water, and a surface tension of a macroscopic solution of the same total composition. When solutions contained a surfactant mass fraction of 0.952, the predicted surface tension throughout hygroscopic growth is reduced relative to the surface tension of pure water (72 mN/m) to 63.5 mN/m and 61.9 mN/m for Triton X-100 and sodium octanoate, respectively. Predictions also showed a 50 nm dry diameter aerosol with surfactant mass fractions of 0.033 and 0.333 were not sufficient to significantly lower the surface tension at cloud droplet activation.